This disclosure relates to print and image systems and in particular to detecting defects in images and printed documents.
In a print system there are common defects that may occur in printed documents. These defects include, for example, image streaking, image banding, excessive graininess, small area deletions and large area deletions. Some existing systems for detecting the defects compare the image of the original electronic document to be printed (reference image) with the image of the printed document (target image) to determine if any differences exist. Some comparison methods are either based on global comparison models, such as SIFT, histogram comparisons and feature vectors, or based on pixel by pixel local differences, such as Structural Similarity Index (SSIM). However, none of these methods can effectively detect the defects in printed documents where the differences between the reference image and the target image are small, colors vary between the reference image and target image, or image alignment between the two is not perfect. For example, some existing methods that compare gray levels between the reference and target images do not perform well given the difficulty of accurately matching the colors. There are also similar issues in detecting defects in an image system, such as detecting defects in a printed or processed image.
This document describes systems and methods that are intended to address at least some issues discussed above and/or other issues.